Current product offerings for cargo and door sensors use such sensors to provide information as to whether the cargo storage area is accessible. Examples of cargo and door sensors can be found in U.S. Pat. Nos. 7,015,824, 7,421,112, and 7,579,941.
The current cargo and door sensors provide a triggering event for the cargo sensor to perform measurements of the cargo area. Motion sensors are often used to determine if there is likely to be load activity, and although this is helpful, it is very imprecise as there are numerous causes for motion which are largely common in their characteristics. However, such solutions for cargo and door sensors employ the cumbersome and costly installation and use of wired or wireless distributed cargo and door sensors, which substantially increases installation time and associated labor cost, increases hardware and maintenance costs, increases the probability of sensor cabling damage, suffers erratic behavior and routine field failures, introduces performance issues which commonly plague solutions which include door sensors, and eventually is rendered useless or is ignored by the consumer.
Early ultrasonic cargo sensors were designed to look for cargo very frequently, (possibly with time-varied sampling), which causes three general problems. (1) Power consumption: Sampling for cargo, based on a schedule, increases power consumption wastefully because samples occur while the load state is static. A typical container or dry van only changes load state 5-10 times per month. The majority of the time the load state is either empty or loaded, and not in transition. Arbitrary sampling of cargo during these long dwells is wasteful in terms of power consumption. (2) Increased latency: Performing cargo samples with a periodic sampling scheme has the opportunity to increase latency, driven by the time between the actual load state change, and the time delay until the next cargo sample is scheduled. Attempting to combat the potential latency with a high rate of sampling can make power consumption dramatically worse. Whereas decreasing the sample rate to combat power consumption can make latency dramatically worse. (3) Event accuracy: Sensing cargo using ultrasonic transducers relies on the stability of the measurement conditions. Changes in the measurement conditions (most notably changes in environmental conditions) can change the results of the measurement, and in some cases, change the resulting determination of the state of the cargo. Examples of this are temperature spikes due to solar loading or rapid increases in humidity due to a rainstorm. These perturbations in the measurement conditions can cause false events to be registered, and while the load state will generally self-correct after the measurement conditions have stabilized, the false events have already occurred.
Thus, there is a need for a system and method configured to overcome the deficiencies of the conventional manner for cargo and door sensors that provides an effective alternative without added installation complexity, and robust field performance for the life of the equipment.